new Windows 7 install won't boot

Hello,
I've been using Vista for awhile now, installed on an IDE HDD (with three 500 GB SATA Seagate drives).
I just bought Win 7 Home Premium and a new 1TB Western Digital Green HDD (SATA).
When I opened my case to install the drive, I smacked my forehead when I realized there are only 4 SATA ports (three taken up by hdd's, and one by my dvd drive). So I swapped out the new WD for an old Seagate, and installed Win 7. Everything went swimmingly, and I installed several apps with no problems, until I restarted and got this after POST:

disk boot failure, insert system disk and press enter

I do this and press enter, and the screen goes black for a second and then repeats the message.
I tried booting from the dvd and choosing repair, but it found no errors with startup. I tried doing a memory test too, and then it booted fine! But once I restarted once more, the same error comes up.
Any ideas?
Thanks in advance!

EVGA nForce 680i
Core 2 Quad 2.5GHz
GeForce 9800GT
4GB ddr 667
1TB WD Green
2x 500GB Seagate

 

EDIT:
I removed completely the IDE drive with Vista on it prior to installing 7.

 

Do a repair install as you changed the MBR by removing the Vista drive.

 

Okay, I removed all devices except my new hdd and the optical drive.
Now it won't even get to the setup portion of the windows disc- I boot from the dvd and it says "loading windows files", then briefly, "starting windows", then crashes to this message:
Windows Boot Manager
Windows failed to start. A recent hardware or software change might be the cause. To fix the problem, insert your windows install disc and restart, (etc)

But restarting just repeats this.
Could it be that my new hdd is bunk?

 

Grab the disk maker's utility and return to factory condition, make a bootable disk with the app and run it, use ImgBurn if you don't already have an ISO burning app. I assume there's nothing of value on the new disk as this will wipe everything.

 

WTF: I unplugged the new drive, and replaced the old system drive with Vista, reset my boot order, and now Vista won't load! What is going on? I specifically bought a new hdd so I could leave my Vista drive alone in case there were problems.
(Thank you for your help!)

 

You mentioned an IDE drive in the mix I believe, I've never had a good experience mixing PATA's and SATA's. The boot always went to the PATA and as that was only a data drive, well no boot eh? Erm, you did set your boot order to DVD first right? Sorry, I had to ask the question as a repair should have worked with W7. I don't know what else to recommend.:confused